The invention relates to devices and methods for treating glaucoma.
Glaucoma is the leading cause of irreversible blindness in the world. It is estimated that 70 million people worldwide have glaucoma, and that nearly 7 million are bilaterally blind from this disease. In the United States, 2.5-3 million people suffer from glaucoma, and it is the third most common reason for adults to visit a medical doctor. Elevated intraocular pressure is the outstanding risk factor for the development of glaucoma, and the main reason for progression of the disease. Accordingly, treatment of glaucoma has been focused on lowering the intraocular pressure in the affected eye.
Glaucoma treatment has customarily comprised a three-step process. First, medicines are tried, such as beta-adrenergic antagonists and alpha-adrenergic agonists. These have proven only moderately, and inconsistently, effective, and can lead to many, sometimes life threatening, side effects, such as respiratory and cardiac side-effects. If medical treatment is either not effective or not tolerated, argon laser trabeculoplasty (ALT) is usually the next step. ALT success is often limited, and is ultimately temporary. The final therapeutic step involves surgery. Trabeculectomy is by far the most common type of surgery done for treatment of glaucoma. It was first described by Cairns in 1969, slightly modified by Watson 1969-71, and has changed little during the last three decades. In a trabeculectomy, a hole is made in the eye near the limbus and into the anterior chamber, under an overlying scleral flap. The aqueous humor thereby is allowed to drain into the subconjunctival space. Subsequent scarring circumscribes this area of subconjunctival drainage into a bleb. Sometimes, the scarring progresses to completely scar down the bleb, stopping the flow of aqueous humor, and causing the surgery to fail. Mitomycin C, an anti-fibroblastic drug, has been used to combat scarring attendant to trabeculoctomy. While increasing surgical success, however, the use of this drug has significantly added to the risks and complications of filtering surgery; mitomycin C causes thinning of the conjunctiva and can lead to leaking through the thinned conjunctiva, and such leaking often leads to hypotony and intraocular infection.
Glaucoma drainage devices (GDD) are an attempt to control the scarring which so commonly tends to seal conduits made in tissue. Molteno, in 1969, described the first of the currently used type of GDD. They consist of a tube and a plate made of synthetic biomaterials. The tube is inserted into the anterior chamber and conducts the aqueous humor to the plate, which is in the subconjunctival space. The problem remains, however, of scarring of the bleb which forms around the plate. About 80% of GDDs appear to be successful for one year, with a 10% additional failure rate each year thereafter. There are significant complications associated with these devices, both in the perioperative and postoperative periods, including hypotony, flat anterior chamber, suprachoroidal hemorrhage, retinal detachment, a hypertensive phase, endophthalmitis, diplopia, corneal decompensation, conjunctival melting, and others. One or more complications have been found to occur in 60-70% of cases.
In one aspect, the invention features a device for treating glaucoma in an afflicted eye. The device includes a body defining a lumen, the body having first and second ends, and external and lumenal surfaces. The body has a length sufficient to provide fluid communication (i.e. the flow of aqueous humor) between the anterior chamber and tear film of the eye when the device is implanted in the sclera. The device further includes a filter capable of providing outflow resistance to aqueous humor flowing through the lumen.
In preferred embodiments, the second end of the device body is adapted to lie, and remain, substantially flush with the scleral surface when the device is implanted in the sclera. The device is preferably flared at the second end to aid in providing an endpoint for the depth of insertion of the device into the sclera.
The body of the device is preferably fabricated from a material selected from the group consisting of silicone, polypropylene, polymethyl methacrylate, and polytetrafluoroethylene.
In preferred embodiments, at least a portion of the external surface of the body is coated with a porous cellular ingrowth coating. Preferably, the porous cellular ingrowth coating is coated on the portion of the device that is in contact with the sclera when the device is implanted. The remaining surfaces of the devicexe2x80x94the entire lumenal surface, the portion of the external surface not in contact with the sclera, and the filter surfaces of the devicexe2x80x94are preferably coated with a bio-inert surface coating.
The filter is preferably a microporous filter membrane. In preferred embodiments, a filter membrane may be fused to the periphery of the body at the lumenal opening at the second end of the body to form a one-piece device for implantation in the sclera. The filter has an inflow face, an outflow face and a peripheral edge. Preferably the peripheral edge of the filter is contiguous with the body of the device, and more preferably is contiguous with the device body at the lumenal opening in the second end of the body. Alternatively, in other embodiments the device may be a unitary article in which a microporous filter membrane is integral with the material used to form the body of the device.
In preferred embodiments of the device, the microporous filter membrane may comprise a silicon(e) or silicon(e)-based microporous filter membrane, a microporous polymer network, a fiber network, or microcapsular material.
Preferably, micropores in the microporous filter membrane have a diameter less than or equal to about 0.2 microns.
The devices of the present invention have a length sufficient to provide fluid communication between the anterior chamber and tear film of the eye when the device is implanted in the sclera. Preferably, the devices have a length of at least about 2.5 mm.
The diameter of the lumen of the device is preferably about 0.5 mm or less. The diameter of the lumen may increase at the second end of the device in those embodiments where the second end of the device is flared.
In preferred embodiments of the devices of the present invention, at least a portion of the external surface of the body, preferably corresponding to the portion of the surface extending into the anterior chamber, all of the surface of the lumen, and the filter surfaces includes a bio-inert surface coating. The bio-inert surface coating may, for example, include phosphoryl choline or polyethylene oxide.
The device preferably may also include at least one barb, preferably extending from the external surface of the device body in the portion of the body in contact with the sclera when the device is implanted. The barb or barbs are adapted to engage with the sclera to provide stability when the device is implanted.
The device is preferably beveled at its first end to aid in the implantation process.
In another embodiment, the device includes, at its second end, a lip extending around at least a portion of the periphery of the second end, the lip having an external lip surface continuous with the external surface of the body. A portion of the external surface of the lip is adapted to contact the external scleral surface of the eye when the device is implanted in the sclera. Preferably, the lip includes a porous cellular ingrowth coating on at least a portion of its external surface, and the lip preferably extends around at least half the circumference of the second end of the device.
In still another embodiment, the second end of the device body includes a head portion having a cavity in communication with the lumen of the body, wherein the head portion has opposing inner and outer faces such that the inner face is in contact with the surface of the eye when the device is implanted, and the outer face includes the filter. The inner surface of the head portion may include a porous cellular ingrowth coating. Preferably, the filter is contiguous, at its peripheral edge, with the peripheral edge of the outer opposing face of the head portion that defines an opening in the cavity.
In another aspect, the invention features a one piece device for treating glaucoma in an afflicted eye. The device includes a body defining a lumen and having first and second ends. The body is of sufficient length to provide fluid communication between the anterior chamber and the tear film of the eye when the device is implanted in the sclera. The device further includes a filter having inflow and outflow faces, and a peripheral edge. At least a portion of the peripheral edge of the filter is contiguous with the body.
In still another aspect, the invention features a method for treating glaucoma in an afflicted eye. The method involves the steps of providing a device as disclosed herein, and implanting the device in the sclera of the eye such that aqueous humor flows from the anterior chamber to the tear film of the eye. In all embodiments of the method, the method involves the step of making an incision into the anterior chamber of the eye prior to implantation of the device. The method may further involve suturing the second end of the device to the sclera following implantation.